Sample injection for analysis



Dec. 22, 1964 SAMPLE INJECTION FOR ANALYSIS Filed June 19, 1961 2r. .TZ

F I I1 lnvenlor 77/0/4/75 50m A's/v r B W,M%s

T. B. KENT 3,1 62,035

United States Patent 3,162,035 SAWLE INJECTIGN FOR ANALYSES Thomas Brian Kent, Norton-on-Tees, England, assignor to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain Filed June 19, 1961, Ser. No. 118,110 Claims priority, application Great Britain, .l'une 22, 1960, 21,348/ 60 4 Claims. (Cl. 7323.1)

This invention relates to analysis of gas or liquid.

The very sensitive analytical techniques which are now available make it possible to analyse a very small sample of gas or liquid. However, the reliability of the results obtained depends on the accuracy with which the volume of the introduced sample may be measured; and how to measure with reasonable accuracy the volume of a very small sample has hitherto been a diflicult problem. The present invention provides an apparatus for reducing this difl'iculty.

According to the present invention a method of introducing a sample of fluid to an analytical device comprises injecting at known intervals of time predetermined volumes of the fluid into a stream of a diluent fluid which is substantially chemically inert to the said sample, the rate of flow of the said stream at any time being known, passing the resulting stream of mixed fluids through at least one mixing vessel and subsequently introducing a measured sample of the mixed fluids to the analytical device.

Whereas the stream of diluent fluid may be intermittent, it is preferably a continuous stream.

The invention includes the use of more than one stage of injection of a sample into a stream of diluent fluid followed by mixing the product obtained, although in practice for most applications of the invention a single stage process usually suii'ices. For example after obtaining a stream of mixed fluids from a single stage process predetermined volumes of fluid from this stream may be injected at known intervals of time into a stream of a diluent fluid, the rate of flow of the latter stream at any time being known, and then introducing a measured sample of the final mixed fluids to the analytical device.

The invention is particularly applicable to chromatography.

The fluid sample and the diluent may be either liquid or gas. For example when the invention is applied to gas chromatography the sample, which may be either liquid or gas, may usually conveniently be injected into a stream of nitrogen.

The diluent fluid stream preferably has a substantially constant rate of flow. The sample is preferably injected into the diluent fluid stream at regular intervals of time.

The means for introducing the fluid sample into the diluent fluid stream may conveniently comprise a device as claimed in British patent specification No. 800,212.

It is preferable to use at least two mixing vessels connected in series, in order to ensure a more uniform mixing of the sample and the diluent.

Each mixing vessel may conveniently comprise a substantially cylindrical chamber having an inlet tube, preferably at one end of the chamber, disposed substantially at right angles to the axis of the chamber and substantially tangentially to its curved surface, and an outlet tube, preferably at the other end of the chamber. The volume of each mixing vessel may be any suitable amount: for example about 3 litres may be convenient.

When the invention is applied to chromatography, a measured sample of the mixed fluids is preferably introduced to the chromatographic column by injecting the sample into a carrier fluid stream of substantially constant velocity which is continuously passed through the column. This injection may conveniently be achieved by using a device according to the invention claimed in British patent specification No. 800,212. The device may be operated once if it is desired to analyse a single sample; or it may be operated at regular time intervals if it is desired continuously to analyse a sample, for example for process monitoring purposes.

In gas chromatography it is often convenient to use argon as the carrier gas.

For a better understanding of the invention, one specific embodiment thereof will now be described with reference to the accompanying drawing wherein:

FIGURE 1 is a schematic flow diagram showing an apparatus for carrying out a method of introducing a liquid sample into a carrier gas stream intended for introduction to a chromatographic column; and

FIGURE 2 is a plan view taken along lines 22 in FIGURE 1 to illustrate the tangential location of the inlet tubes to each chamber of FIGURE 1 and to illustrate a suitable location for each outlet tube.

Referring now to FIGURE 1, a continuous stream of the sample liquid A is introduced to a valve B of the type claimed in British patent specification No. 800,212, and passes to Waste at C. A diluent gas stream D is also passed through the valve B. This valve is operated at regular intervals of time to transfer known volumes of the sample into the diluent gas stream. The resulting stream E comprising diluent and vaporised sample is passed through a mixing vessel F, and the stream G, I

whose components have been mixed, is passed into another mixing vessel H. The more thoroughly mixed stream I emerging therefrom is passed through a second valve 1 of the type claimed in British patent specification No. 800,212. This stream is passed to waste at K; and a continuous stream of carrier gas L is passed through the valve J. This valve is operated once, or at regular time intervals as desired, in order to inject a measured sample (or measured samples at regular time intervals as the case may be) from stream 1 of diluted original sample into the carrier gas stream M which is introduced to a chromatographic column.

As an example of the present invention suppose it were desirable to introduce 0.0001 ml. of a gas sample into a chromatographic column. Using conventional techinques it is difiicult to measure with reasonable accuracy the volume or" a sample of less than about 0.01 ml. However, using this invention, 1.0 ml. of the sample could be injected ten times per minute into a diluent gas stream of velocity 990 ml./min. The resulting stream, after being thoroughly mixed by passing through two mixing vessels in series, may then be passed through a valve capable of injecting 0.01 ml. of the mixture into a stream of carrier gas. As the mixture contains 1% by volume of the sample, this means that 0.0001 ml. of the sample will be injected into the carrier gas, which is passed through the chromatographic column. A similar technique may conveniently be applied to a liquid sample, which is vaporised at an appropriate temperature and injected into a stream of diluent gas. In this case also, the concentration of the sample in the mixed stream of gases may readily be calculated. It will be appreciated that an analogous method may also be used in connection with liquid chromatography, where it is desired to inject a liquid sample into a stream of diluent liquid.

I claim:

1. An apparatus for introducing a sample fluid to an analytical device comprising first conduit means for a continuous stream of diluent fluid; first valve means for introducing predetermined volumes of said sample fluid at known-intervals of time into the continuous stream of diluent fluid in said first conduit means, said diluent fluid being substantially chemically inert to the said sample fluid, the rate of flow of said diluent stream at any time being known; at least one mixing vessel; second conduit means for continuously passing the resulting stream of combined fluids through said mixing vessel to thoroughly mix the fluids; third conduit means for convey ng a continuous stream of carrier gas to said analytical device; second valve means for subsequently introducing a measured amount of the mixed fluids into the continuous stream of carrier gas in said thirdc-onduit means, said third conduit means thereafter introducing the combined stream of mixed fluids and carrier gas into said analytical device.

2. An apparatus according to claim 1 wherein the predetermined volumes of sample fluid are supplied to said first valve means from conduit means for a continuous stream of said sample fluid.

3. An apparatus according to claim 1 wherein each mixing vessel comprises a substantially cylindrical chamher having an inlet tube disposed substantially at right angles to the axis of the chamber and substantially tangentially to its curved surface, and an outlet tube.

4. An apparatus according to claim 1 including at least two mixing vessels connected in series.

v01. 4, February 1954, pages 82-85.

Article by Simmons et a1. published in Analytical Chemistry, vol. 30, No. 1, January 1958, pages 32-35.

Book, Keulemans, Gas Chromatography, Reinhold lublishing (30., N.Y., secondedition, 1959, page 70.

Article by De Wet et al. published in Analytical Chernistry, vol. 32, N0. 2, February 1960, pages 169-172.

RECHARD C. QUEISSER, Primary Examiner.

20 ROBERT EVANS, Examiner". 

1. AN APPARATUS FOR INTRODUCING A SAMPLE FLUID TO AN ANALYTICAL DEVICE COMPRISING FIRST CONDUIT MEANS FOR A CONTINUOUS STREAM OF DILUENT FLUID; FIRST VALVE MEANS FOR INTRODUCING PREDETERMINED VOLUMES OF SAID SAMPLE FLUID AT KNOWN INTERVALS OF TIME INTO THE CONTINUOUS STREAM OF DILUENT FLUID IN SAID FIRST CONDUIT MEANS, SAID DILUENT FLUID BEING SUBSTANTIALLY CHEMICALLY INERT TO THE SAID SAMPLE FLUID, THE RATE OF FLOW OF SAID DILUENT STREAM AT ANY TIME BEING KNOWN; AT LEAST ONE MIXING VESSEL; SECOND CONDUIT MEANS FOR CONTINUOUSLY PASSING THE RESULTING STREAM OF COMBINED FLUIDS THROUGH SAID MIXING VESSEL TO THOROUGHLY MIX THE FLUIDS; THIRD CONDUIT MEANS FOR CONVEYING A CONTINUOUS STREAM OF CARRIER GAS TO SAID ANALYTICAL DEVICE; SECOND VALVE MEANS FOR SUBSEQUENTLY INTRODUCING A MEASURED AMOUNT OF THE MIXED FLUIDS INTO THE CONTINUOUS STREAM OF CARRIER GAS IN SAID THIRD CONDUIT MEANS, SAID THIRD CONDUIT MEANS THEREAFTER INTRODUCING THE COMBINED STREAM OF MIXED FLUIDS AND CARRIER GAS INTO SAID ANALYTICAL DEVICE. 